1. Field of the Invention
The present invention pertains to methods for depositing high quality films of complex (compound) materials on substrates at high deposition rates, and apparatus for effecting such methods. More particularly, the present invention pertains to photo-enhanced chemical vapor deposition (PECVD) methods for depositing high quality, stoichiometrically-correct, thin films of a large variety of complex compounds at high deposition rates, and computer controlled apparatus for effecting such methods.
2. Description of the Relevant Art
There are known methods for depositing thin films of complex compounds such as metal oxides, ferroelectrics, superconductors, materials with high dielectric constants, gems, etc. Such known methods include RF sputtering, chemical vapor deposition (CVD) and spin coating processes.
The known methods, however, have many problems and disadvantages associated therewith. For example, with RF sputtering methods most commercially available target sources have significant quantities of impurities therein so that even before you begin the sputtering process there is a significant chance of failure due to the impurities in the target source. Further, it is difficult to control chemical proportions of materials deposited in a sputtering process so that a thin film which is eventually deposited has many variations of chemical composition therethrough and across the surface thereof.
Spin deposition processes of complex thin films usually involve two primary steps. An initial step of spinning a stabilized liquid source, such as a sol-gel, onto a substrate, and a second step of drying the liquid spun onto the substrate. The initial step of spinning liquid onto a substrate is usually done in the open environment, which undesirably permits the liquid to absorb impurities (including moisture) from the environment. Further, the drying step of the process is rather violent due to the evaporation of organic precursors from the liquid, which leaves damaging pores (or pop holes) in the thin film.
With regard to known CVD processes, significant disadvantages are associated with the handling of the raw materials that are injected into a CVD reactor inasmuch as these materials are usually very toxic and the Environmental Protection Agency has imposed very strict standards for handling of these materials, which makes such handling both difficult and expensive. Further, the reactive nature of known CVD depositions (in which two or more vaporized components are reacted and then deposited on a substrate) is generally hard on the CVD reactor itself, so that the reactor must be constructed to withstand the reactions and must often be maintenanced at considerable cost. Relatedly, it is very difficult to consistently deposit stoichiometrically correct, multiple-component thin films using presently available CVD equipment.
Additionally, CVD processes and subsequent annealing processes, which are required with many thin films, such as ferroelectrics, are normally operated at relatively high reactor temperatures, which tends to damage the thin films and the substrates onto which they are deposited. Damage to the thin films include removal of certain critical elements (such as lead) therefrom; formation of pores, secondary phases, and large grains; and serious non-stoichiometry.
One known modification to the CVD processes is to add a means of photo-enhancement as a secondary heating means for inducing chemical reactions of the vaporized compounds within the CVD reactor. Such known photo-enhancement techniques reduce some of the problems associated with CVD processes, but are still insufficient for depositing high quality, stoichiometrically correct thin films of many complex compounds in a practical, commercially-viable manner.
The present invention has been developed to overcome the many problems and disadvantages associated with known deposition techniques for depositing thin films of complex compounds including those discussed above, and to generally fulfill a great need in the art by providing a production worthy process which can be used to produce a large variety of high quality, complex thin films.